Rock securing method

ABSTRACT

Method for securing rock faces by compound build-up in underground or open pit mining is described in which curable resin is injected to a bore hole through a plastic covering layer.

United States Patent Rotter 1 1 July 8, 1975 [54] ROCK SECURING METHOD 3,283,513 11/1966 Kierans et a1. 61/45 8 3,332,244 7/1967 McLean 52/309 [751 Invenm" Kaprun 3,430,449 3/1969 Novotny et a] 61/45 B Austna 3,487,533 1/1970 Striim 52/378 3,716,386 2/1973 Kempster et 106/93 [73] Asslgnee gf 'ggg 3,721,094 3/1973 Elders et al 299/11 [22] Filed: July 24, 1973 Primary ExaminerPaul R. Gilliam [2]] App!" 3823 Assistant Examiner-Alex Grosz [30] Foreign Application Priority Data July 25, 1972 Germany 2236457 [57] ABSTRACT [52] U.S. Cl. 61/45 B; 299/11 [51] Int. Cl. E0lg 5/10 Method for securing rock faces by compound build-up [58] Field of Search 61/45 B, 35, 45 R; 52/378, in underground or open pit mining is described in 52/309; 299/1 1, 10 which curable resin is injected to a bore hole through a plastic covering layer. [56] References Cited UNITED STATES PATENTS 6 Claims, 2 Drawing Figures 2,110,053 3/1938 Phillips 106/91 ROCK SECURING METHOD BACKGROUND OF THE INVENTION It is known to build anchors in mountains by filling bore holes or existing rock cracks with hardenable plastic, preferably a polyester or epoxy resin, with if necessary reinforcement by glass fibers or the like. Austrian Pat. No. 236,321. It is also known that such plastics can be injected in liquid form under pressure into bore holes to stabilize mine roofs. US. Pat. No. 3,260,053. The plastic allegedly adheres to the mountain, even under the presence of water. Special formulations are described in British Pat. No. 868,873.

Film-forming plastics are also used for lining mine tunnels, with fillers such as ground quartz being added to the plastics. German Publ. No. 1,170,351.

Up to now reinforced concrete anchors and a spray concrete layer have been used as a compound build-up for mountain faces which are to be secured. Schweizerische Bauzeitung, 75. year 1957, book 9, pages I23 to l3l; Gluckauf I (I904), book 9, pages 490 to 501.

The mountain consolidation attainable by such compound provides only a single effect. The anchoring attained by reinforced concrete in the bore holes and by a layer of spray concrete adhesively applied to the mountainside in order to prevent the breaking of the mountain areas between the anchors do not yield under local load differences; i.e., the materials hold immovably up to their breaking point with no elastic behavior. Furthermore the strength of cement mortar used for anchor securing and surface solidification is not very high.

An earlier invention described in German Application No. P2l048l5.7-24 involves compound build-up as a mountain solidification technique in underground mining and in open-pit mining. Broadly in this method, bore holes are drilled into a mountain surface at appropriate intervals, the walls of which are roughened and cleaned, if necessary, and into which a plastic is pressed. The plastic is applied in liquid form but cures to great strength. A closing head at the mountainside is formed with the plastic which fills the bore holes. This is accomplished by way of a moulding hood. A sealing layer consisting of a mixture of sand and plastic is applied to the surface of the mountain over the closing heads after removal of the moulding hood.

DESCRIPTION OF DRAWINGS FIG. I is a schematic illustration, in section, of a mountain wall treated in accordance with the present invention; and

FIG. IA is a schematic illustration, in section, of an alternative embodiment of the invention.

DETAILED DESCRIPTION The prior art problems of mountain solidification are solved according to the invention by applying plastic mortar as a cover layer to the smoothed mountain wall prior to the drilling of the bore holes, drilling the bore holes through the cover layer and moulding a frustrocone-shaped closing head at each plastic plug.

By applying the cover layer of plastic and sand mixture prior to drilling the bore holes for the plastic anchors. reinforcement is provided and no portion of the mountain is lost by breaking during the drilling of the LII bore holes. Moreover, water which may spring from the mountain is dammed off. In addition, an intimate connection of the plugs with the cover layer is achieved during the compound build-up as a result of the joining of the frustrocone-shaped closing heads of the plastic plugs with the cover layer during curing of the injected plastic, providing a binding between the mountain and the cover layer.

To prepare the mountain wall, a spray concrete preferably containing steel fibers such as pieces of fine wire is applied in the desired thickness. The plastic mortar can have glass fibers admixed therewith so that its strength is further increased and in the same manner the plastic of the plugs can contain glass fibers or other reinforcing fibers. Moulded fiber glass rods can also be inserted into the bore holes prior to the introduction of the plastic.

This method results in a homogeneous rock layer down to the depth of the bore holes, that is a fully solidified surface yet which can yield in itself. The elastic properties of the plastic permits equalization of local tensions without destruction of the compound buildup. It is not possible to create such a homogeneous formation by using such materials as steel and cement. Furthermore sealing against mountain waters or inside waters in water tunnels is achieved by the method according to the invention. Depending upon the kind and thickness of the surface and depth of securing, inside and outside water pressures, i.e. compressionand tension stresses, can be endured.

The entire technique can be locally adapted to any given mountainside. Thus in case of alternating solid and slidable mountain surfaces, fewer bore holes of a smaller diameter and less depth and a cover layer of less thickness are needed for the firm rock, while in the adjacent slidable mountainside, a more thorough consolidation is achieved by the use of deeper and larger bore holes, and by the earlier application of a thicker cover layer. Joining the plugs with the cover layer by means of the closing heads results in a homogeneous and elastic mountain surface.

FIG. I shows schematically in section one embodiment of the compound build-up according to the invention. The mountain wall I is obtained by blasting or milling the desired cavity out of the mountain. The unevenness of wall 1 is smoothed by applying a layer of spray concrete 2 of from approximately 1 to 10 cm. To increase the strength of this layer, it is possible to admix steel fibers of a diameter of between 0.1 and 0.3 cm and a length of between 1.5 and 2.5 cm with the spray concrete. Over this smoothing layer is applied cover layer 3 of plastic mortar. If wall I of the mountain is already very smooth, layer 2 of spray concrete can be omitted, so that the cover layer 3 consisting of plastic mortar would be applied directly. To increase the strength of cover layer 3, glass fibers of l to 2.5 cm length are, for example, admixed to cover layer 3, so that the percentage of plastic therein is from about 20 to about 30 percent. Thereafter bore hole 4 is drilled, the spacing, depth and diameter of which or the optional use of well tubing depends upon the particular mountain condition and quality. Head 5 of hole 4 in cover layer 3, and optionally in concrete layer 2 and, if necessary, in the mountain surface as well is coneshaped.

Over head 5, injection cover 6 is sealingly applied. Thereafter the plastic is injected in liquid form under pressure through an orifice in cover 6 until it fills bore hole 4 and any crevasses 11 extending sideways from the bore hole. A plastic plug is thus obtained after curing of the plastic, for example in 4 to 5 hours.

Optionally an injection of water can be performed after drilling of bore hole 4 for cleansing purposes. The desired adhesive result will not be diminished by this with the appropriate selection of a water compatible plastic.

The plastic can be mixed with glass fibers 9, or a fberglass rod 8 in the shape of a porous tubing can be inserted to increase the strength of the plug.

After curing the moulding head with the pressure injection device is removed.

The materials used can be varied widely and are selected in order to deflect tensions across the walls of a mountain which is being secured. Thus for example, in rocks having a geological modulus of elasticity (elastic deformation) of from 3,000 to 30,000 kg/cm, it is desirable to employ synthetic materials having a modulus of elasticity of from 20 to 40,000 kg/cm As noted above, glass fiber, which demonstrates a typical modulus of elasticity of from 50 to 70,000 kg/cm, can be admixed with the plastic. Typical plastics which can be used for example as the covering layer include epoxide and polyester resins. This can be modified through the incorporation of ground minerals such as quartz or sand of a particle size upto 0.2 mm and in a ratio of from about l:2 to about 1:4. The injectable plastic which forms the plug can for example be a rapidly curing epoxide resin.

The following examples serve the purpose of illustrating the invention.

EXAMPLE 1 ln tunnel construction in underground mining, firmly standing to fragile rock at the ceiling and tunnel wall must be fortified. A smoothing layer of spray concrete having a thickness of from 5 to cm is applied. A cover layer of polyester resin is next applied to a depth of l to 1.5 cm. Bore holes of a diameter of 30 to 50 mm are drilled to a depth of between 3 to 4 m at median spacings of 1.2 to 1.5 m. These are then filled with curable plastic.

EXAMPLE 2 A slightly broken to much fractured rock formation is to be reinforced. A smoothing spray concrete layer of 5 to 15 cm is applied according to need. Cover layer 3 of plastic mortar is applied to a thickness of L5 to 2 cm. The diameter of the plastic plug varies between 40 and 50 mm, the length thereof between 3.5 and 4.5 m, while the spacing between the plugs is from l to L2 m.

EXAMPLE 3 In a tunnel construction, a rock formation must be reinforced. The rock comprises sediments, much destroyed rock and rolling and sandy components. The smoothing spray concrete layer is applied to between 10 and 20 cm. The thickness of cover layer is between 2 and 2.5 cm. The diameter of the plugs varies from 40 to mm, the length thereof from 4 to 6 m, and the spacing between the plugs 0.8 and 1.0 m.

EXAMPLE 4 In an open pit, a securing wall is needed. The smoothing layer is applied to the mountain wall at a thickness of from ID to 15 cm. The cover layer consists of plastic mortar having a thickness of l to 1.5 cm. The diameter of the plugs varies from 40 to 50 mm, the length thereof varies from 3 to 5 m and distances between the plugs varies from 1.0 to 2 m.

For Example I, a suitable injection pressure for the plastic is 5 atmospheres (gauge); for Example 2 up to 3.5 atm and for Example 3 up to 2 atm.

What is claimed is:

1. In the method of securing rock faces in which a curable plastic resin is injected into holes in the face, the improvement which comprises applying a covering layer of curable plastic to the face prior to boring the holes, boring the holes through the covering layer into the rock face with a frustroconical shape so that the diameter of the hole on the surface of the covering layer is greater than the diameter of the bore shaft, injecting a curable plastic resin under pressure into the holes so that the hole is filled with curable plastic resin in the bore shaft and in the frustroconical portion, curing the curable plastic of the covering layer, and curing the curable plastic resin in the holes to form a plurality of plastic plugs in said holes having frustroconical portions in close contact with the covering layer, whereby said covering layer is securely held against the rock face by the frustroconical portions of the plastic plugs.

2. The method according to claim I wherein concrete is sprayed on said rock face prior to application of said covering layer.

3. The method according to claim 1 wherein said covering layer comprises a mixture of curable resin, sand and glass fibers.

4. The method according to claim 1 wherein said injected plastic resin is reinforced with glass fibers.

5. The method according to claim 1 wherein said injected plastic resin is reinforced with plastic fibers.

6. The method according to claim 1 wherein fiberglass rods are inserted into said bore holes prior to injecting said curable resin. 

1. In the method of securing rock faces in which a curable plastic resin is injected into holes in the face, the improvement which comprises applying a covering layer of curable plastic to the face prior to boring the holes, boring the holes through the covering layer into the rock face with a frustroconical shape so that the diameter of the hole on the surface of the covering layer is greater than the diameter of the bore shaft, injecting a curable plastic resin under pressure into the holes so that the hole is filleD with curable plastic resin in the bore shaft and in the frustroconical portion, curing the curable plastic of the covering layer, and curing the curable plastic resin in the holes to form a plurality of plastic plugs in said holes having frustroconical portions in close contact with the covering layer, whereby said covering layer is securely held against the rock face by the frustroconical portions of the plastic plugs.
 2. The method according to claim 1 wherein concrete is sprayed on said rock face prior to application of said covering layer.
 3. The method according to claim 1 wherein said covering layer comprises a mixture of curable resin, sand and glass fibers.
 4. The method according to claim 1 wherein said injected plastic resin is reinforced with glass fibers.
 5. The method according to claim 1 wherein said injected plastic resin is reinforced with plastic fibers.
 6. The method according to claim 1 wherein fiberglass rods are inserted into said bore holes prior to injecting said curable resin. 